Method of making a toroidal core-coil combination with in situ molded end rings

ABSTRACT

A toroidal core-coil combination has a core comprising a toroidal body formed of magnetic material and having a central opening therethrough and ends. End rings formed of insulating plastic material are molded in situ on each of the ends substantially covering the axially exposed surfaces thereof, each end ring having an exposed surface provided with a series of grooves circumferentially exposed therearound. The coil comprises a wire conductor wound on the body in turns passing through the central opening, the turns being received in and located by the grooves. The dimensions of the grooves and the conductor are so related as to permit such winding and enable such location of the turns. In the process for manufacturing the toroidal core-coil combination, the end rings are molded either simultaneously or successively. In the latter instance, one of the end rings is molded and the grooves formed therein, and then the resultant sub-assembly is placed in a mold which uses the grooves for rotatably fixing the position of the sub-assembly in the mold, the second of the end rings then being molded in the mold. A layer of insulating plastic material may also be molded on a radially exposed inner or outer surface of the body simultaneously with the molding of one or both of the end rings.

United States Patent [191 Gostyn et al.

[ Jan. 14, 1975 METHOD OF MAKING A TOROIDAL CORE-COIL COMBINATION WITHIN SITU MOLDED END RINGS [75] Inventors: Ernest Gostyn, El Paso, Tex.;

Francis J. Fratar, Springfield, Mass.

[73] Assignee: General Instrument Corporation,

Newark, NJ.

[22] Filed: Nov. 12, 1973 [21] Appl. N0.: 414,978

[52] US. Cl 29/605, 242/4 R, 335/210,

[51] Int. Cl. H011 7/06 [58] Field of Search 335/210, 213; 29/605; 242 4R [56] References Cited UNITED STATES PATENTS 3,512,233 5/1970 Mancini29/605 X 3,559,134 1/1971 Daley 29/605 X 3,757,262 9/1973 Over et al.335/210 X 3,758,888 9/1973 Kadota 335/210 3,801,941 4/1974 Phillips335/210 Primary Examiner-G. Harris [57] ABSTRACT A toroidal core-coilcombination has a core comprising a toroidal body formed of magneticmaterial and having a central opening therethrough and ends. End ringsformed of insulating plastic material are molded in situ on each of theends substantially covering the axially-exposed surfaces thereof, eachend ring having an exposed surface provided with a series of groovescircumferentially exposed therearound. The coil comprises a wireconductor wound on the body in turns passing through the centralopening, the turns being received in and located by the grooves. Thedimensions of the grooves and the conductor are so related as to permitsuch winding and enable such location of the turns.

In the process for manufacturing the toroidal core-coil combination, theend rings are molded either simultaneously or successively. In thelatter instance, one of the end rings is molded and the grooves formedtherein, and then the resultant sub-assembly is placed in a mold whichuses thegrooves for rotatably fixing the position of the sub-assembly inthe mold, the second of the end rings then being molded in the mold. Alayer of insulating plastic material may also be molded on a radiallyexposed inner or outer surface of the body simultaneously with themolding of one or both of the end rings.

11 Claims, 18 Drawing Figures PATENTEU J 1 4 I975 SHEET 10F 3 METHOD OFMAKING A TOROIDAL CORE-COIL COMBINATION WITH IN SITU MOLDED END RINGSBACKGROUND OF THE INVENTION In order to obtain predictable andreproducible control of the magnetic field within the opening of atoroidally wound ferro-magnetic core, the turns of the winding must bedisposed in predetermined locations and secured there throughout thelife of the core. In the early state of the art this was accomplished bythe formation of grooves or channels in the annular core itself (byabrasion or cutting of the core material) and subsequent laying of thewinding turns in such grooves. However, as the ferro-magnetic corematerial is extremely brittle in nature, great care had to be exercisedin the precision machining of such grooves, and the grooving process wasaccordingly both time consuming and laborious. Furthermore, as theferro-magnetic core material may be an electrical conductor, electricalinsulation had to be provided between the core and the windings toinsure proper operation of the wound core and to reduce the possibilityof short circuits.

To remedy the aforementioned defects, in the curreent state of the artthe core grooves are replaced by grooved plastic end rings whichareaffixed on the ends of the core and provide with grooves to receiveand secure the turns of the winding. While providing a significantimprovement over machined core grooves, the use of grooved plastic endrings has not proven to be entirely satisfactory in operation for anumber of reasons. Great care must be taken to insure proper axialseparation of the end rings and proper registration of the grooves ofone end ring with the grooves of the other end ring. To insure properspacing of the end rings on the core, it is generally necessary toprecision machine the outer surface of the core at both ends so that theend rings can be slipped onto the core and press-tit towards one anotheruntil the proper axial separation is obtained. If for mechanical orelectrical reasons the end rings are to extend part way into the annularopening of the core, machining of the portion of the inner surface ofthe core to be covered by the end ring is also required. Furthermore, asthe two end rings differ considerably in diameter, alignment of thegrooves of the two end rings requires a precise indexing or registrationassembly technique.

A further disadvantage of this system is the continuing need to providea layer of insulating material about the core to insulate it from thewinding, the application of the insulating material typically being anadditional step in the process. Furthermore, if the layer of insulatingmaterial extends all the way to the end rings, as required for completeprotection, it tends to interfere with the proper placing of the'endrings on the core. Typically in order to insure maintanence of theproper spacing and registration of the end rings during the subsequentwinding step and throughout use of the wound core, it is considereddesirable to utilize an adhesive cement to secure the end rings in placeon the core. Each of the above steps for applying and securing the endrings on the core is further complicated by the inherent fragility ofthe end rings.

Accordingly, it is another object of the present invention to provide atoroidal core-coil combination in which proper axial spacing of the endrings and registration of the grooves thereof are invariably obtainedand retained, all without precision machining of the core structure orthe use of adhesives.

It is another object of the present invention to provide such a toroidalcore-coil combination in which a layer of insulating material may beprovided between the coil and core, integral with one or both of the endrings and without requiring an additional process step.

It is also an object of the present invention to provide such a toroidalcore-coil combination having a simple and rugged construction which isdurable in use and able to withstand repeated shocks and jostlingwithout modification of the spacing and registration of the end rings.

A further object of the present invention is to provide a method ofmaking a't oroidal core-coil combination which insures proper axialspacing of the end rings and registration of the grooves of one end ringwith the grooves of the other end ring. 1

to obtain and secure proper spacing and registration of the end rings.

' Yet another object of the present invention is to providesuch a methodwhich permits an insulating layer of material to be applied to a radialsurface of the core simultaneously with the formation of one or both ofthe end rings.

SUMMARY OF THE INVENTlON It has now been found that the above andrelated objects of the present invention are provided in a toroidalcoil-core combination including a core comprising a toroidal body formedof magnetic material and having a central opening therethrough and ends.End rings formed of insulating plastic material molded in situ on eachof the ends substantially cover the axially exposed surfaces thereof,each end ring having an exposed surface provided with a series ofgrooves circumferentially exposed therearound. The coil comprises a wireconductor wound on the body in turns pssing through the central opening,the turns being received in and located by the grooves. The dimensionsof the grooves are so related to the dimensions of the conductor as topermit such winding and enable such location of the turns.

In a preferred embodiment, a layer of the insulating plastic material isdisposed on a radially exposed surface of the body and extends from atleast one of the end rings. The layer is molded in situ integrally withthe aforementioned at least one end ring, and preferably both of the endrings. The layer may be disposed on the inner or outer radial surface ofthe body and may cover only a minor fraction of the area of that surfaceor substantially all of such surface of the body.

The body is generally in the form of a frustrum, and the body ends andthe end rings are preferably provided with interlocking parts. Thegrooves of the end rings may be disposed at least in part on theradially exposed surfaces of the end rings, or at least in part onaxially exposed surfaces of the end rings; preferably they are disposedat least in part on both radially and axially exposed surfaces of theend rings.

The method of making the toroidal coil-core combination comprises thesteps of providing a toroidal body formed of magnetic material having acentral openingand a wire conductor is wound around the body in turnswhich are received in and circumferentially located by the grooves. Thedimensions of the grooves are so related to the dimensions of theconductor as to ,fjl permit such winding and enable such location of theturns. v I

The end rings may be molded simultaneously or se- "quentially, and thegrooves may be formed in the end rings either during molding of the endrings or after the.

' end rings have been molded. A layer of the insulating plastic materialmayalso be molded on the radially exposed surface of the bodysimultaneously with the molding of one or both of the end rings, thelayer being molded on either the inner or outer surface of the body andcovering either a minor fraction or substantially all of such surface.

In a preferred embodiment of the method, first one of the end rings ifmolded and the grooves formed therein. Subsequently the resultantsub-assembly is placed in a mold which uses the grooves for rotativefixing the position of the sub-assembly in the mold, the second of theend rings then being molded in the mold and the grooves thereof beingformed simultaneously.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation view, incross section, showing a mold suitable for use in forming in situ on atoroi dal core body the end rings of the present invention;

FIG. 2 is a side elevation view of the toroidal core with in situ moldedend rings (as formed in the mold of FIG. 1);

FIG. 3 is a front elevation view of the core taken along the line 3-3 ofFIG. 2;

FIG. 4 is a rear elevation view of the core taken along the line 4-4 ofFIG. 2;

FIG. 5 is a fragmentary sectional view, to an enlarged scale, takenalong the line 5-5 of FIG. 3, and shows the interlocking nature of thefront or large end ring and the front of the core body;

FIG. 6 is a fragmentary sectional view, to an enlarged scale, takenalong the line 6-6 of FIG. 4 and shows the interlocking nature of therear or small end ring and the rear of the core body;

FIG. 7 is a side elevation view of a core according to the presentinvention having grooved end rings and 'three strips of insulatingmaterial extending between the end rings on the outer surface of thecore body;

FIG. 8 is a front elevation view taken along the line 8-8 of FIG. 7, andschematically indicates representative winding of a coil on the core;

FIG. 9 is a rear elevation view taken along the line 9-9 of FIG. 7, andschematically indicates representative winding of a coil on'the core;

FIG. 10 is a fragmentary section view, to an enlarged scale, taken alongthe line l0-10 of FIG. 8, and shows the interlocking relationshipbetween the front or large end piece and the front of the core body (oneturn of the coil being indicated in phantom line);

FIG. 11 -is a fragmentary front elevation view, to a greatly enlargedscale, of the front end ring taken along the line 11-11 of FIG. 10;

FIG.l2 is a fragmentary top plan view, to a greatly enlarged scale, ofthe front end ring taken along the line l212 of FIG. 10;

FIG. 13 is a fragmentary sectional view, to an enlarged scale, takenalong the line 13-13 of FIG. 9, and shows the interlocking relationshipbetween the rear or smaller end ring and the rear end of the core body(one turn of the coil being indicated in phantom line);

FIG. 14 is a fragmentary rear elevation view,to a greatly enlargedscale, taken along the line l4- 14 of FIG. 13;

FIG. 15 is a top plan view of the rear end ring, to a greatly enlargedscale,.taken along theline 15-15 of FIG.13;-

FIG. 16 is a perspective view of an insulated core according to thepresent invention having three strips of insulating material on theinner surface thereof extendoverall viewing of theme construction;

FIG. 17 is a perspective view of an insulated core according to thepresent invention having a layer of insulating material completelycovering the outer surface of the core body between theend rings, thegrooves of the core being omitted to facilitate overall viewing of thecore construction; and

FIG. 18 is a perspective view of an insulated core according to thepresent invention having a layer of insulating material completelycovering the inner surface of the core body between the end rings, thegrooves of the core being omitted to facilitate overall viewing of thecore construction.

DETAILEDDESCRIPTION OF THE PREFERRED EMBODIMENTS invention. Morespecifically, the core 10 comprises a toroidal'core body 12 with acentral opening 14 therethrough, a large or front end 16, and a smalleror rear end 18. Thecore body 12 has the general configuration of anannular frustrum and is formed of suitable magnetic material such as theferro-magnetic compound conventionally used for electrical cores intransformers and the like. Molded in situ on the core body 12 are a pairof end rings; the large or front end ring 26 substantially covers theaxially exposed surface of the large or front end 16 of the core body12, and the smaller or rear end ring 28 substantially covers the axiallyexposed surface of the smaller or rear end 18 of the core body 12. Theend rings 26, 28 are formed of electrically insulating plastic materialof either a thermoplastic nature (such as polypropylene, polyethylene,and polystyrene) or a thermosetting nature (such as the phenolics andpolyesters).

Referring now to FIG. 1, therein illustrated is a two part injectionmold generally designated by the numeral 30 and having a right half 34,aleft half 32 and openings 36, 38 which communicate respectively withcavities 40, 42 therein to permit the injection of plastic insulatingmaterial from without the mold 30 into the cavities 40, 42. Inoperation, the core body 12 is placed in the right half 34 of the openmold 30, the mold is s'ecurely closed by affixing left half 32 to righthalf 34, and the desired plastic insulating material is injected throughinjection openings 36, 38 into end ring cavities 40, 42, respectively,to mold in situ on the core body ends 16, 18 the end rings 26, 28respectively. The mold halves 32, 34 are finally opened to permitremoval of the core with in situ molded end rings 26, 28. As the detailsof injection molding are well known in the art, there is no need to gointo the detailed operating parameters'of the injection molding process.It will also be noted, however, that the configuration and dimensions ofthe surfaces of the core body ends 16, 18 eventually covered by the endrings 26, 28 are not critical (as in prior art processes usingindependently fabricated end rings) as deviations therein areautomatically adapted to by the end rings 26, 28 as the latter aremolded in situ on the former. The end rings 26, 28 formed in situ by themolding process are strongly bonded directly to the core body ends 16,18 and require no adhesives to secure them thereto. As the end ring pairis formed in a single operation using a single mold 30, it will beobvious that the desired spacing between the end rings 26, 28 (and theappropriate registration of any grooves thereon) will be easily,infallibly and automatically obtained in a single step due to theinherent precision of the injection molding operation.

While the strength of the bonds occuring between the plastic end rings26, 28 and the core body ends 16, 18

is generally sufficient to preclude rotative play of the end rings 26,28 on the core body ends 16, 18, in instances where it is expected thatthe toroidal core-coil combination will be subjected to unusually largeor repeated vibrations or jarring, a mechanical interlock arrangementmay be provided between the core body ends 16, 18 and the end rings 26,28 to insure that proper spacing and registration of the end ring pairis maintained. FIG. 5 illustrates a suitable mechanical interlockbetween the large end ring 26 and the large core body end 16, while FIG.6 illustrates a suitable mechanical interlock between the small corebody end 18. In both instances, the core body ends 16, 18 are formedwith a circumferential pattern of axiially-extending inward recesses ordepressions 50 as well as axiallyextending peripheral tabs orprojections 52. The end ring 26, 28 will naturally and automatically beformed, as part of the molding process, with a series of correspondinginward bulges or projections 54 to fill the recesses or depressions 50of the core body ends 16, 18 and a series of axially-extending recessesor depressions 56 to receive the peripheral tabs or projections 52 ofthe core ends l6, 18. In this manner not only is the total frictionaland bonding area between the mating surfaces of the end rings 26, 28 andthe core body ends l6, 18 increased, but an actual physical interlock isprovided to guarantee that the end rings 26, 28 are not rotatablerelative to the core body ends 16, 18 in the absence of an actualbreaking of each of the mating elements 50-54 and 52-56. Generally abouteight sets of mating elements 50 and 54, 52 and 56 regularly spaced 45apart about each end ring-core body end set are used, although a greateror lesser number may be used for particular applications.

As will be immediately apparent to those skilled in the art, the endring pair may be molded in situ onto the core body 12 using aconventional plastic injection mold having an interior surface which isthe negative of any desired shape for the core 10. Thus the desiredcomplex surface of-the core 10 with the required wireguiding grooves,electrical insulating layers and dimensional characteristics are simplyobtained in a single process step, with the desired end ring spacing andgroove registration being insured by the precision of the mold.Accordingly, while the illustrated mold 30 is adapted to produce thecore 10 illustrated in FIGS. l-6 and characterized both by the absenceof grooves on the end ring pair and by the absence of layers or stripsof insulative plastic material on the core body 12 between the end ringpair, it is obviously a simple matter to modify the design of theinterior of the mold 30 to produce the core 10 of FIG. 7, which core 10is characterized both by the presence of registering circumferentiallyexposed grooves on exposed surfaces of the end ring pair and by thepresence of a plurality of bridging strips of insulative plasticmaterial on the outer radial surface of the core body 12 integral withand exbridging strips 70 of plastic insulating material extending overthe outer surface of the core body 12 between the end ring pair.Referring now in particular to FIGS. 78 and l012, a plurality ofcircumferentially exposed grooves 76 substantially cover the exposedaxial and radial surfaces of the front end ring 26, Referring now inparticular to FIGS. 7 9, and l3-l5, a plurality of circumferentiallyexposed grooves 78 substantially cover the exposed axial surface of therear end ring 28. While FIG. 7 illustrates a preferred pattern ofgrooves 76, 78, other patterns will be useful for particularapplications and for different configurations of the core body 12.Generally the grooves 76, 78 are disposed at least in part on radiallyexposed surfaces of the end rings, or at least in part on axiallyexposed surfaces of the end rings, the larger end ring 26 (andsometimesthe smaller end ring 28) usually having grooves disposed at least inpart on both the radiallyand the axially exposed surfaces thereof. I

A wire conductor 80 is wound on the core 10 in turns passing through thecentral opening 14 thereof and being received in and located by thegrooves 76, 78 of the front and rear end rings 26, 28, respectively. Thedimensions of the grooves 76, 78 are so related to the dimensions of theconductor 80 as to permit such winding and enable such locations of theturns. The grooves 76, 78 not only facilitate the initial winding of thecore 10 with the conductor 80, but also insure that the turns of theconductor 80 remain in place despite any vibrations or shock to whichthe toroidal core-coil combination may be subjected in use (so long asthe conductor 80 remains intact and unstretched).

The pattern of the winding of conductor 80 on the core 10 is determinedby the desired function of the to roidal core-coil combination, and thewinding illustrated in the drawing is to be taken only as exemplary ofone of the many patterns which may be utilized. By way of example, aplurality of separate wire conductors 80 may be utilized to provide thedual toroidal deflection yoke used in the cathode ray or picture tube ofa television set. It is to be noted, however, that the grooves 76, 78 ofthe core 10 permit the standard core 10 to be wound in any of amultitude of patterns, with the turns of the winding passing through thecentral opening 14 of the core body 12 and being received in and locatedby the grooves 76, 78 in a secure and reliable fashion. While therepresentative winding illustrated in FIGS. 8-10 and 13 shows a singlegroove receiving only a single turn of the conductor 80, it will beobvious that one or more turns of the conductor 80 could also bereceived in and located by a single groove 76 or 78. Where a largenumber of turns of the conductor 80 are to be received by a singlegroove 76, 78, the dimensions of the grooves 76,78 may be increased toaccommodate the'dimensions of the accumulated turns passingtherethrough. Furthermore, while the illustrated small end ring 28 hasgrooves 78 only on its exposed axial surface, obviously communicatinggrooves could also be provided on its exposed radial surface forparticular applications.

If desired, the configuration of the mold 30 which receives the corebody 12 may be modified (and the mold possibly provided with one or moreadditional injection openings) to permit the molding of one or morelayersor strips 70 of insulating plastic material on the inner and/orouter radial surfaces of the core body 12 simultaneously with themolding of one or both of the is integral therewith. Such a layer 70 mayextend over one complete inner or outer surface'of the core body, andpreferably both the inner and outer surface thereof, between the endring pair and be integral with the end ring pair 24 to preclude anypossibility of electrical shorting involving the core body 12 and theconductor 80. Alternatively, the mold 30 may be modified to provide forthe molding (in situ and simultaneously with the molding of at least oneof the end rings 26 or 28, and preferably both) of one or more strips 70of plastic insulating material extending on the inner and- /or outerradial surfaces of the core body 12 from such at least one end ring andintegral therewith. Preferably the strips extend between and areintegral with both end rings 26, 28, such'bridging strips 70 permittingthe attachment of extaneous electrical componenets such as circuitboards to the toroidal core-coil combination in a convenient manner.Thus, the insulating plastic material may be applied as an inner layercovering substantially all of the inner radial surface of the core body(as shown in FIG. 18), as an outer layer covering substantially all ofthe outer radial surface of the core body (as shown in FIG. 17) ormerely as strips or other patterns integral with at least one of the endrings 26, 28 (preferably both) and covering only a minor fraction of asurface of the core body 12; for example, as strips extending betweenthe end rings 26, 28 on the inner radial surface of the core body 12 (asshown in FIG. 16) or on the radial surface of the core body 12 (as shownin FIG. 7).

The grooves 76, 78 may be formed in the end rings 26, 28 in severaldifferent ways. Where possible, the simplest technique is obviously toform the grooves 76, 78 as part of a single molding operation formingboth end rings 26, 28 simultaneously, as described hereinbefore. Anothertechnique is to mold both blank or ungrooved end rings 26, 28 in asingle molding operation (as shown in FIGS. I-6) and then form thegrooves 76,

78 therein in a single post-molding machining operation. By way ofexample, a stepping motor may be used to progressively rotate the coreby angular increments as a phased-in-time cutting tool machines thedesired grooves 76, 78 by conventional embossing,

' broaching or cutting techniques. A third technique is to I moldingoperation or in a separate machining operation) and then utilize thegrooved end ring to index the location of the partial core in a secondmold where the other end ring and its grooves are formed in a singleseparated molding operation. More specifically, one end ring(hereinafter arbitrarily referred to as end ring 26) is formed first ina molding process using a mold 30 similar to that shown in FIG. 1 exceptthat there is only one opening 36 and one cavity 40. Grooves 76 may beformed on the single end ring 26 as part of the molding operation, or,alternatively, the partially formed core (that is, the core body 12 witha single end ring 26) may be removed from the mold 30 and machined toprovide the desired grooves 76' on the end ring 26. In either case, thepartially formed core (including a single grooved end ring 26) is placedin a second mold provided with a modified cavity 40characterized byinterior projections which engage the machined grooves 76 of the singleend ring 26 to rotatively and axially fix its position within the secondmold, and hence the position of core body 12 within such mold. Thesecond mold is further provided with an opening 38 and cavity 42 forsimultaneously forming not only the other end ring, but also the grooves78 thereof. Molding the second grooved end ring 28 in this mannerinsures both that the appropriate spacing between the end rings 26, 28is achieved and that the grooves 76, 78 of the various end rings 26, 28are formed in proper registration.

Thus it can be seen that the present invention pro vides a toroidalcore-coil combination in which proper axial spacing of the insulatingplastic end rings and registration of the grooves thereof are invariablyobtained and retained, all without precision machining of the corestructure or the use of adhesives. Furthermore, the present inventionpermits a layer or strips of plastic insulating-material to be placed onthe core body integral with one or both of the end rings and withoutrequiring an additional process step. Because the end rings (and anydesired layers or strips of plastic insulating material) are molded insitu on the toroidal core body, a simple and rugged construction isprovided which is durable in use and able to withstand repeatedvibrations and shocks without modification of the spacing andregistration of the end rings.

The present invention is directed primarily and especially towards thepeculiar problems of winding toroidal-magnetic deflection yokes, whereby virtue of opposing fluxes in the core there is obtained a magneticfield within a central opening of limited diameter passing through thecore body; however, the principles of the present invention are alsoapplicable in a broader sense to such other toroidal structures asindicators and transformers, where the magnetic field is intended to becontained within the ferro-magnetic material of the core body.

Now that the preferred embodiments of the present invention has beenshown and described in detail,'varione or more cavities adjacent themain cavity and comcavities and fed by a separate opening, to provide adis tinctive pattern of insulative plastic material on the radialsurface of the core body. Such a pattern of plastic insulative materialis retained on the radial surface of the core body through bondingalthough it is not integral with either of the end rings. Also, the endrings may be formed in situ on the core body ends using casting ratherthan injection molding techniques. Accordingly, it is to be understoodthat the spirit and scope of the present invention is to be limited notby the foregoing disclosure, but only by the appended claims.

We claim:

1. The method of making a toroidal core-coil combination comprising thesteps of A, providing a toroidal body formed of magnetic material andhaving a central opening therethrough and ends;

B. molding in situ onto each of said ends an end ring of insulatingplastic material which substantially covers at least the axially'exposedsurface of the corresponding body end;

C. forming registering grooves in an exposed surface of each of said endrings; and

D. winding a wire conductor around said body in turns which are receivedin and circumferentially located by said grooves, the dimensions of saidgrooves being so related .to the dimensions of said conductor as topermit such winding and enable such location of said turns.

2. The method of claim 1, in which said end rings are moldedsimultaneously.

' 3; The method of claim 1, in which said grooves are formed in said endrings during molding of said end rings.

4. The method of claim 1, in which said grooves are formed in said endrings after both of said end rings have been molded.

5. The method of claim 1, in which first one of said end rings is moldedand the grooves formed therein, and then the resultant sub-assembly isplaced in a mold which uses said grooves for rotatively fixing theposition of said sub-assembly in said mold, said second of said endrings being molded in said mold and the grooves thereof being formedsimultaneously.

6. The method of claim 5, in which said grooves are formed in said firstof said end rings simultaneously with the molding thereof.

7. The method of claim 1, in which a layer of said insulating plasticmaterial is molded on a radially exposed surface of said bodysimultaneously with the molding of one of said end rings.

8. The method of claim 7 in which said layer is molded on the innersurface of said body.

9. The method of claim 7, in which said layer is molded on the outersurface of said body.

10. The method of claim 2, in which a layer of said insulating plasticmaterial is molded on a radially exposed surface of said bodysimultaneously with the molding of both of said end rings.

11. The method of claim 1 wherein said toroidal body is a toroidalmagnetic deflection yoke.

1. The method of making a toroidal core-coil combination comprising thesteps of A. providing a toroidal body formed of magnetic material andhaving a central opening therethrough and ends; B. molding in situ ontoeach of said ends an end ring of insulating plastic material whichsubstantially covers at least the axially exposed surface of thecorresponding body end; C. forming registering grooves in an exposedsurface of each of said end rings; and D. winding a wire conductoraround said body in turns which are received in and circumferentiallylocated by said grooves, the dimensions of said grooves being so relatedto the dimensions of said conductor as to permit such winding and enablesuch location of said turns.
 2. The method of claim 1, in which said endrings are molded simultaneously.
 3. The method of claim 1, in which saidgrooves are formed in said end rings during molding of said end rings.4. The method of claim 1, in which said grooves are formed in said endrings after both of said end rings have been molded.
 5. The method ofclaim 1, in which first one of said end rings is molded and the groovesformed therein, and then the resultant sub-assembly is placed in a moldwhich uses said grooves for rotatively fixing the position of saidsub-assembly in said mold, said second of said end rings being molded insaid mold and the grooves thereof being formed simultaneously.
 6. Themethod of claim 5, in which said grooves are formed in said first ofsaid end rings simultaneously with the molding thereof.
 7. The method ofclaim 1, in which a layer of said insulating plastic material is moldedon a radially exposed surface of said body simultaneously with themolding of one of said end rings.
 8. The method of claim 7 in which saidlayer is molded on the inner surface of said body.
 9. The method ofclaim 7, in which said layer is molded on the outer surface of saidbody.
 10. The method of claim 2, in which a layer of said insulatingplastic material is molded on a radially exposed surface of said bodysimultaneously with the molding of both of said end rings.
 11. Themethod of claim 1 wherein said toroidal body is a toroidal magneticdeflection yoke.